The invention relates to a sleeve assembly for refurbishing a submerged fuel rack employed to temporarily store fresh or spent nuclear fuel assemblies and more particularly to a sleeve assembly which may be readily installed in (or extracted from) an existing fuel rack without having to remove the rack from the pool in which it is submerged.
Fresh and spent nuclear fuel assemblies employed in commercial nuclear power plants for generating electric power are stored temporarily in cells of fuel racks submerged in water pools until such time as they are to be transported elsewhere. Spent fuel assemblies may need to be stored in such racks for several years. See, e.g., U.S. Pat. Nos. 4,630,738; 4,960,560; 5,245,641; 5,311,563 and 5,905,770. Spent fuel racks may have 100 or more open ended vertical cells generally formed of vertically oriented thin metal plates supported at their bottom edges by a horizontal base plate. The vertically oriented plates may contain boron or other neutron absorbing materials. Alternatively, certain of the vertically oriented walls may be covered with neutron absorbing plates. After years of use, the fuel racks may need to be refurbished.
The nuclear industry has found that, after years of service, some of neutron absorbing plates are deteriorating in the water pools in which the racks are submerged. Thus, the nuclear industry desires to refurbish these existing fuel racks. The industry has considered: mechanical refurbishment of the racks, entire replacement of the racks and fuel assembly covers. Mechanical refurbishment is a very complicated time-consuming procedure and undesirably requires removing the racks from the fuel pools. Entire replacement of the racks may take two years from design through installation. Also, replacement requires that the original racks must be removed from the pools and either decontaminated and free-released or processed and sent to a low-level radioactive waste burial site. In addition, it has been proposed to cover individual spent fuel assemblies with neutron absorbing plates. However these spent fuel assembly covers must always remain with the fuel assemblies and present handling/disposal problems when the spent fuel is transferred to dry fuel storage or a repository.
It is an object of the present invention to provide a fuel rack refurbishment that may be readily installed and/or extracted at any time. It is a further object to provide a refurbishment that can be readily performed in the fuel pool without having to remove the racks.
With these objects in view, the present invention resides in a sleeve assembly for refurbishing a fuel rack having cells in which fresh or spent nuclear fuel assemblies may be stored, which cells are defined by elongate walls extending from a rack base plate. The rack base plate has flow holes extending therethrough communicating with the interior portions of the cells for permitting pool water to flow into the cells and cool the fuel assemblies. The sleeve assembly includes a sleeve having at least one elongate wall (preferably containing neutron absorbing material if neutron absorption is of concern) extending from one side of a sleeve base having two opposed sides and the sleeve base has a flow hole extending therethrough. A pin assembly is disposed in the sleeve base flow hole and has at least one resilient tab extending beyond the second side of the sleeve base for extending into a rack base plate flow hole and engaging the rack base plate when the sleeve assembly is installed in one of the cells.
In a preferred embodiment of the sleeve assembly, the pin assembly has a tubular portion that fits in the sleeve base hole and a plurality of resilient tabs that extend beyond the second side of the sleeve base plate. Preferably, each tab has an intermediate section with a surface facing and extending parallel to the second side of the sleeve plate for resiliently engaging the rack base plate when the tabs extend into a rack base plate hole. Advantageously, the resilient tabs of the pin assembly may engage the walls of the rack base plate hole and the bottom surface of the rack base plate hole so that movement of the sleeve assembly is restricted both horizontally and vertically. In addition, such a structure permits water to flow through the sleeve base flow hole into a cell at all times, permits a sleeve assembly removal tool to be readily lowered through the center of the flow hole and manipulated to release the resilient tabs and extract the sleeve assembly, and permits an inspection device such as a CCD camera to inspect the condition of the resilient tabs. See, in this regard, U.S. Pat. No. 5,305,356 to Brooks et al. which discusses the use of a CCD (Charge Coupled Device) video camera to inspect nuclear power plants.